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SHORT REPORT Open Access
Differential pathogenicity of two differentrecombinant PVYNTN
isolates in Physalis floridanais likely determined by the coat
protein geneXinxi Hu1, Xianzhou Nie2*, Changzheng He1 and Xingyao
Xiong1
Abstract
A previous study has identified two types of recombinant
variants of Potato virus Y strain NTN (PVYNTN) in Chinaand
sequenced the complete genome of the variant PVYNTN-HN2. In this
study, the complete genome of isolatePVYNTN-HN1 was fully sequenced
and analyzed. The most striking difference between the two variants
was thelocation of recombinant joint three (RJ3). In PVYNTN-HN1,
like other typical European-PVYNTN isolates such asPVYNTN-Hun, the
RJ3 was located at nucleotide (nt) 9183, namely the 3’ proximal end
of the CP gene (nt. 8571-9371), thus leading to most (the first 613
nucleotides from the 5’ proximal end) of the CP gene (801 bp) with
aPVYN origin and PVYN-serotype; whereas in contrast, the RJ3 in
PVYNTN-HN2 was located at nt 8572, consequentlyleading to a CP gene
of PVYO origin and PVYO-serotype. The varied genome composition
among PVYO, PVYN, PVYN:O, PVYNTN-HN1 and PVYNTN-HN2 made them
useful for the investigation of possible roles of gene segment(s)
insymptom formation on host plants. When Physalis floridana plants
were infected with different PVY isolates, twotypes of symptoms
were induced. PVYN and PVYNTN-HN1 induced mild symptoms (mainly
mild mottling) whereasPVYO, PVYN:O and PVYNTN-HN2 induced serve
symptoms including leaf and stem necrosis, leaf-drop and
stunting.These results, together with a previous study using
artificial PVY chimeras, demonstrate that the CP gene,
especiallythe 5’ proximal segment (nt 8572-9183), and/or CP likely
determine the pathogenicity of PVY in P. floridana.
FindingsPotato virus Y (PVY) is the type species of the
Potyvirusgenus in the Potyviridae family [1]. It infects a numberof
plant species in the nightshade family (Solanaceae)and causes a
wide range of symptoms from symptomlessto mosaic, mottling,
lesions, stunting, necrosis and plantdeath, depending on the plant
species, the cultivar, thevirus strain and isolate [1]. PVY
possesses a single-stranded positive RNA genome comprised of
approxi-mately 9700 nucleotides that encode a polyprotein
ofapproximately 3061 amino acids [2]. The polyproteinundergoes
proteolysis to form 10 mature proteins withdifferent functions
including replication, transportationand spread of the virus [1,2].
Many strains/substrains ofPVY have been recognized according to the
primaryhosts and host reactions. For the potato-infecting PVY,the
ordinary strain (PVYO), the tobacco veinal necrosis
strain (PVYN) and the potato stipple streak strain(PVYC) are the
first ones to be recognized [1], followedby the potato tuber
necrosis strain (PVYNTN) and therecombinant N:O/Wilga group (PVYN:O
or PVYN-Wilga) [3-5]. PVYNTN is characterized by its ability
toinduce potato tuber necrotic ringspot disease (PTNRD)in sensitive
potato cultivars [5-7], whereas PVYN:O isdefined by its reaction to
PVYO-specific antibody (i.e.,PVYO-serotype) but causing veinal
necrosis on tobaccoplants (i.e., PVYN pathotype) [5,8]. Two types
ofPVYNTN, one recombinant and the other non-recombi-nant, have been
identified [4,7,9]. The former is repre-sented by PVYNTN-Hun [10]
and has been referred to asEuropean (Eu)-PVYNTN [7,11-13], and the
latter isrepresented by PVYNTN-Tu 660 [7] and has beenreferred to
as North American (NA)-PVYNTN
[7,11,12,14]. Both Eu-PVYNTN and NA-PVYNTN react toPVYN-specific
antibody [11,13]. Recently, a new recom-binant PVYNTN variant type
has been identified in Syria[15,16] and China [9]. The variant type
that includes theisolates PVYNTN-NW [16] and PVYNTN-HN2 [9]
reacts
* Correspondence: [email protected] Research Centre,
Agriculture and Agri-Food Canada, P.O. Box 20280,850 Lincoln Road,
Fredericton, New Brunswick, E3B 4Z7, CanadaFull list of author
information is available at the end of the article
Hu et al. Virology Journal 2011,
8:207http://www.virologyj.com/content/8/1/207
© 2011 Hu et al; licensee BioMed Central Ltd. This is an Open
Access article distributed under the terms of the Creative
CommonsAttribution License
(http://creativecommons.org/licenses/by/2.0), which permits
unrestricted use, distribution, and reproduction inany medium,
provided the original work is properly cited.
mailto:[email protected]://creativecommons.org/licenses/by/2.0
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to PVYO-antibody and induces veinal necrosis ontobacco and PTNRD
on sensitive potato cultivars [9,16].Reverse transcription-PCR
(RT-PCR) based genotypinghas been successfully used to characterize
the genomefeatures of the Eu-PVYNTN-like isolate PVYNTN-HN1and the
PVYNTN-NW-like isolate PVYNTN-HN2 in China[9]. Here we report the
differential responses of Physalisfloridana to PVYNTN-HN1 and
PVYNTN-HN2 infections.PVYNTN-HN1 and PVYN induced mottling on P.
flori-dana whereas PVYNTN-HN2, PVYO and PVYN:O
induced severe symptoms including leaf and stemnecrosis,
leaf-drop and stunting. The results, togetherwith the genome
make-ups of various PVY isolates, sug-gest that the CP gene plays a
significant role in symp-tom induction in P. floridana, consistent
with theresults reported by Bukovinszki et al. [17].The greenhouse
maintained PVY isolates PVYNTN-
HN1 (formerly PVY sample 1 [9]), PVYNTN-HN2,PVYN-Jg, PVYO-RB and
PVYN:O-Mb58 in ‘Russet Bur-bank’ plants/tubers [5,7,9,11-13] were
used in this study.PVYNTN-HN1 and PVYNTN-HN2 were obtained inChina
[9], while the rest were from Canada [5,7,11-13].All isolates have
been characterized molecularly by P1gene- and recombinant joint
(RJ)-based RT-PCR assays[12,13], pathologically by tobacco- and
potato-basedbioassays, and serologically by PVYO- and
PVYN-anti-body-based ELISA assays [5,7,9,11-13,18]. Moreover,except
for PVYNTN-HN1, all of the isolates have beensequenced fully
(PVYNTN-HN-2, PVYN-Jg, PVYO-RB) orpartially (PVYN:O-Mb58)
(accession numbers areHM367076, AY166867, GQ200836, AY745493
forPVYO-RB, PVYN-Jg, PVYNTN-HN-2, and PVYN:O-Mb58respectively). To
better understand the isolate PVYNTN-HN1, especially to reveal the
exact nucleotide locationsof the recombinant joints that had been
detected by RT-PCR [9], the complete genome of PVYNTN-HN1
wassequenced. The same nine sets of PCR primers (for pri-mer
sequences, see reference [7]) that had been used toclone/sequence
various isolates of PVY [5,7,9,18] wereused. Each primer pair
resulted in a DNA fragment of1.0 to 1.3 kb, overlapping with
adjacent fragments withapproximately 100 bp at each end. Each
fragment wascloned into a pGM-T cloning vector (TIANGEN Bio-tech,
Beijing, China) according to the manufacturer’sinstructions; and
two clones of each fragment weresequenced from both forward and
reverse directionsusing the universal T7 promoter and SP6-promoter
pri-mers at the Sangon Biological Engineering Technology&
Services Co. Ltd (Shanghai, China). The completegenome sequence
(GenBank accession numberHQ631374) was confirmed by re-sequencing
overlappingcDNA clones obtained from a separate experiment fromRNA
isolated from PVYNTN-HN1 infected tobaccoleaves. Sequence
identities were analyzed using BLAST
(http://www.ncbi.nlm.nih.gov/BLAST). For detection ofthe
recombinant events, complete nucleotide sequencesof various PVY
isolates were aligned using
ClustalW2(http://www.ebi.ac.uk/Tools/clustalw2/index.html) [19].The
aligned sequences served as inputs for similarityscanning using the
program SimPlot [20, generously pro-vided by the author at
http://sray.med.som.jhmi.edu/].The resulting similarities were
plotted along the nucleo-tide sequences of the virus genome.As
anticipated, PVYNTN-HN1 shared highest sequence
identities with PVYNTN-Hun, a representative of
typicalEu-PVYNTN, at both complete nucleotide and polypro-tein
levels at 99.2% and 99.1%, respectively. It was fol-lowed by
PVYNTN-HN2/PVYNTN-NW, PVYN:O, PVYN
and PVYO, represented by isolates PVYNTN-HN2, PVYN:O-Mb112,
PVYN-N605 and PVYO-RB, respectively(Table 1). The sequence
identities between PVYNTN-HN1 and PVYN-Jg, a NA- PVYN [7,11], were
90.9% and95.9% at the complete nucleotide and polyprotein
levels,respectively (Table 1). As expected, the sequence
identi-ties between PVYNTN-HN1 and PVYN:O-Mb58 (acces-sion number
AY745493, partial length) were similar tothat between PVYNTN-HN1
and PVYN:O-Mb112 (datanot shown). Further comparison of PVYNTN-HN1
withPVYNTN-HN2 at mature protein level revealed that thetwo shared
high sequence identities for all proteins (97.8- 100%) but the CP
(Table 1), which was similar to thatexhibited in PVYNTN-Hun vs
PVYNTN-HN2 [9].Sequence screening of PVYNTN-HN1 against PVYO
(e.g.,PVYO-RB) and PVYN (e.g., PVYN-605 or PVYN-Jg) usingSimPlot
[20] revealed three recombinant joints at nt2419, 5844 and 9183 in
PVYNTN-HN1 genome (Figure1D), resulting from the genome
recombination betweenPVYN and PVYO. In contrast, the RJs in
PVYNTN-HN2were located at nt 2521, 5867 and 8572 (Figure 1D)
[9].PVYNTN-HN1 shares identical RJs with PVYNTN-Hun(data not
shown). The location of RJ3 in PVYNTN-HN1and PVYNTN-Hun at nt 9183,
namely the 3’ proximalend of CP gene (nt 8571-9371), led to most
(the first613 nt from the 5’ proximal end) of the 801-bp-long
CPgene of a PVYN origin, which eventually resulted in
aPVYN-serotype of these isolates [5,7,9]. In contrast, theRJ3 in
PVYNTN-HN2/PVYNTN-SYR-NB-16N (accessionnumber AB270705) at nt 8572,
namely the 5’end of theCP gene, led to the complete CP gene of a
PVYO origin,which further resulted in a PVYO-serotype [9,15].
OneRJ, namely RJ1, was present in PVYN:O isolates
includingPVYN:O-Mb112 and PVYN:O-Mb58 at nt 2397 [5] (Fig-ure 1D),
resulting in a recombinant genome in whichthe segment prior to the
RJ was from PVYN and theremainder from PVYO [5].Previous study has
revealed the pathotypes of
PVYNTN-HN1 and PVYNTN-HN2 on tobacco and potato[9]. To further
characterize the biological properties of
Hu et al. Virology Journal 2011,
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http://www.ncbi.nih.gov/entrez/query.fcgi?db=Nucleotide&cmd=search&term=HQ631374http://www.ncbi.nlm.nih.gov/BLASThttp://www.ebi.ac.uk/Tools/clustalw2/index.htmlhttp://sray.med.som.jhmi.edu/
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these isolates, and, moreover, to investigate whether
thedifferent RJ3 sites, namely different CP gene types, playa role
in symptom induction in different plant species,tobacco (cv.
‘Samsun’), potato (cv. ‘Yukon Gold’) andPhysalis floridana plants
were mechanically inoculatedwith PVYNTN-HN1, PVYNTN-HN2, PVYN-Jg,
PVYO-RB,and PVYN:O-Mb58 as described previously [9].
Mock(buffer)-inoculated plants were used as a healthy con-trol. As
shown in Figure 1A, petiole and stem necrosisoccurred on tobacco
plants 15 days after inoculationwith PVYN-Jg, PVYN:O-Mb58,
PVYNTN-HN1 orPVYNTN-HN-2. Veinal necrosis also developed on
theseplants. On the other hand, the PVYO-infected plantsonly
developed mosaic symptoms on the leaves andwere free of veinal,
petiole and stem necrosis (Figure1A). No symptoms were observed on
the mock-inocu-lated plants. Various studies have indicated that
HC-Proplays an important role in necrosis development ontobacco
plants [5,21,22]. All isolates but PVYO-RB pos-sessed a PVYN-type
of HC-Pro gene [5,7,9,18] (Figure1D), and therefore induced
PVYN-like symptoms includ-ing veinal/petiole/stem necrosis on
tobacco plants.When inoculated to ‘Yukon Gold’ plantlets
(5-leaf-stage), the isolates induced varied foliar
symptomsincluding mild mottling (PVYN-Jg), mosaic (PVYN:O-Mb58) and
severe mosaic/stunting/leaf deformation(PVYO-RB, PVYNTN-HN1 and
PVYNTN-HN2) (data notshown), consistent with the previous report
[9]. No visi-ble symptoms were observed on potato tubers
producedfrom plants infected with PVYN-Jg, PVYO-RB or PVYN:O-Mb58;
and in contrast, distinct necrotic ringspotswere observed on potato
tubers harvested from plantsinfected with PVYNTN-HN1 or PVYNTN-HN2
(Figure
1B), thus confirming that both types of recombinantPVYNTN
isolates are capable of inducing PTNRD in sen-sitive potato
cultivars.It has been known that PVYO induces necrosis in Phy-
salis floridana, whereas PVYN incites mottling in thisspecies
[1]. Using N/O hybrids comprised of the chi-meric genome of
PVYN-N605 [23] and PVYO, the symp-tom formation on P. floridana due
to PVY infection wasmapped to the CP gene region [17]. Because of
the var-ied genome compositions among the isolates (Figure1D), they
could be used to investigate the putative roleof genome segment(s)
of PVY in symptom developmenton P. floridana, as done on tobacco
[5,24]. Severe symp-toms including leaf and stem necrosis,
leaf-drop andstunting were observed on P. floridana plants
infectedwith PVYO-RB, PVYN:O-Mb58 and PVYNTN-HN2 threeweeks after
inoculation (Figure 1C), and as time pro-gressed, the symptoms
became more distinct. The iso-late PVYN:O-Mb58 led to plant death
five weeks afterthe inoculation. On the other hand, mild
symptoms,mainly mottling, were observed on PVYN-Jg andPVYNTN-HN1
infected P. floridana plants (Figure 1C).Taken together, it can be
concluded that the CP geneoriginated from PVYO is likely
responsible for the severesymptoms in PVYO-, PVYN:O- or
PVYNTN-HN2-infectedP. floridana plants. These results, together
with theresults obtained using artificial PVY chimeras
[17],demonstrate that the CP gene, especially the 5’
proximalsegment (nt 8572-9183) of the gene, plays a critical rolein
symptom formation in P. floridana upon PVY infec-tion, and
determines the pathoginicity of PVY isolates.The 3’ proximal
segment of NIb gene (nt 8136-8570)does not appear to be involved in
the symptom
Table 1 Identities between isolate PVYNTN-HN1 and other isolates
of Potato virus Y (PVY) at both nucleic acid andprotein levels
Length Sequence Identity (%) (Nucleic acid, Protein)
Gene nucleotide,size (bp)
Proteinsize (aa)
PVYO-RB(HM367076)
PVYN-605(X97895)
PVYN-Jg(AY166867)
PVYNTN-Hun(M95491)
PVYN:O-Mb112(AY745491)
PVYNTN-HN2(GQ200836)
5’ UTR 1-188, 188 - 66.0, - 100, - 85.6, - 100, - 100, - 99.5,
-
P1 189-1013, 825 275 73.0, 71.3 99.3, 99.6 92.2, 91.3 98.7, 98.2
99.6, 100 98.9, 100
HC-Pro 1014-2408, 1395 465 82.2, 90.5 98.8, 99.4 92.6, 96.8
99.1, 99.1 98.4, 99.4 98.4, 98.9
P3 2409-3503, 1095 365 97.3, 98.6 84.7, 92.6 84.6, 92.3 99.4,
99.7 99.1, 99.7 96.3, 97.8
6K1 3504-3659, 156 52 97.4, 100 81.4, 84.6 82.1, 86.5 99.4, 100
100, 100 98.1, 98.1
CI 3660-5561, 1902 634 97.3, 99.1 84.1, 95.7 84.1, 95.7 99.6,
99.5 99.3, 99.5 98.7, 99.7
6K2 5562-5717, 156 52 95.5, 100 82.1, 90.4 79.5, 90.4 100, 100
100, 100 99.4, 98.1
VPG 5718-6281, 564 188 86.9, 92.0 97.0, 99.5 95.6, 97.3 98.9,
99.5 87.8, 94.7 97.9, 99.5
NIa 6282-7013, 732 244 80.9, 93.6 99.3, 98.2 97.0, 98.8 99.2,
98.8 80.6, 92.2 99.0, 99.2
NIb 7014-8570, 1557 519 83.5, 93.6 98.8, 99.0 97.6, 98.7 98.7,
98.7 84.9, 94.4 98.2, 99.0
CP 8571-9371, 801 267 90.8, 92.9 97.5, 98.9 96.5, 98.9 99.4,
98.9 91.4, 94.4 91.6, 94.0
3’ UTR 9372-9702, 331 - 98.2, - 84.0, - 85.8, - 99.1, - 98.8, -
99.1, -
Fulllength
1-9702, 9702 3061 87.9, 92.8 93.2, 97.3 90.9, 95.9 99.2, 99.1
94.1, 97.4 97.7, 98.7
Hu et al. Virology Journal 2011,
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formation in P. floridana as suggested by Bukovinszki etal.
[17]. It is also noteworthy that the different symp-toms incited by
different PVY types/isolates in tobacco,potato and P. floridana can
be used to uncover the gen-ome compositions of the virus.
AcknowledgementsThe research was supported by the Ministry of
Science and Technology ofChina under the project # 20073346 to XX
and CH and by Agriculture andAgri-Food Canada (AAFC) under the
projects #50 and #1389 to XN. XH wasa receipt of the Ministry of
Education of China-AAFC Ph.D. StudentInternship Program
(2007-2008); XN is an adjunct professor at HunanAgricultural
University.
Author details1Hunan Provincial Key Laboratory of Crop Germplasm
Innovation andUtilization, Hunan Provincial Engineering Research
Center for Potatoes,College of Horticulture and Landscape, Hunan
Agricultural University,Changsha, Hunan 410128, China. 2Potato
Research Centre, Agriculture and
Agri-Food Canada, P.O. Box 20280, 850 Lincoln Road, Fredericton,
NewBrunswick, E3B 4Z7, Canada.
Authors’ contributionsXH carried out the experiments. XN
designed, analyzed and wrote thepaper. HC and XX collected isolates
PVYNTN-HN1 and PVYNTN-HN2,participated in experiment planning and
execution. All authors read andapproved the final manuscript.
Competing interestsThe authors declare that they have no
competing interests.
Received: 22 November 2010 Accepted: 7 May 2011Published: 7 May
2011
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doi:10.1186/1743-422X-8-207Cite this article as: Hu et al.:
Differential pathogenicity of two differentrecombinant PVYNTN
isolates in Physalis floridana is likely determined bythe coat
protein gene. Virology Journal 2011 8:207.
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